From all the German islands in the North Sea, I would say Sylt has the most megalithic-related sites, only Rügen in the Baltic Sea has probably more.
But you are right, as Sylt is only accessible via ferry (from Denmark) or car train (from Germany), I would stay for a longer period and not only because of the megalithic sites as the island as a lot more to offer.
Some fabulous sites, I hadn't realised Sylt had so much to offer, well worth the difficulty of getting there
From all the German islands in the North Sea, I would say Sylt has the most megalithic-related sites, only Rügen in the Baltic Sea has probably more.
But you are right, as Sylt is only accessible via ferry (from Denmark) or car train (from Germany), I would stay for a longer period and not only because of the megalithic sites as the island as a lot more to offer.